We propose the creation of an HIV neurobehavioral Research Center (HNRC under the aegis of the School of Medicine of the University of California At San Diego, (UCSD). Collaborating with UCSD will be investigators from the Naval Hospital, San Diego, the San Diego VA Medical Center, Scripps Clinic and Research Foundation, The Salk Institute, San Diego State University, and the University of Southern California. The broad goals of the HNRC are to examine the etiology, pathogenesis, natural history, and features of neurobehavioral disturbance associated with HIV infection. We define neurobehavioral broadly as embracing phenomena which can be appreciated by neurologic examination, neuropsychometry, brain imaging, electrophysiology, psychiatric assessment, and neuropathology. These general objectives will be addressed through a set of core assessments of 500 HIV antibody positive (HIV+) and negative (HIV-) men, to be conducted semi-annually for a period of five years. Subjects will include Navy members who have undergone routine HIV screening, among whom will be a unique group of 200 dated seroconverters. To these 200 will be added 90 undated Navy HIV carriers and 50 HIV- controls from the Navy. A sample of at risk civilians will also be examined, of whom 120 will be HIV+ and 40 HIV-. Added to the core assessments will be more detailed studies of selected subjects by a set of projects which will probe more deeply into neurological, psychiatric, risk factors, and predictive mathematical models. The significance of the HNRC derives from the importance of understanding the neurobehavioral correlates of HIV both for clinical and public policy determination; from the comprehensive scope of the multidisciplinary approach to neurobehavioral issues; from the collection of an unusually strong group of biobehavioral scientists from many disciplines, and from the availability of a unique sample of unselected, dated seroconverters from the U.S. Navy.